There were people reading the ability in different ways, therefore the FAQ has standing to settle the issue.
Right and wrong.
Firstly, the actual, strict RaW cannot, in the specific circumstance, mean more than one thing (if you'd like a reminder why, PM me please, I don't want to sidetrack this thread
too much), so there is nothing to clarify from that angle.
At best, then, the FaQ entry (assuming it still had the same goal) could only (legitimately) be a RaI or houserule entry, even if it only specifically handled Deepwarden.
However, the FaQ entry instead addresses Max Dex bonuses in general, and blatantly contradicts the RaW (which again, remember, it has no power to change) without actually noting itself as a RaI/suggestion note.
This is very bad form for the FAQ.
Just because someone reads or hears something doesn't mean that's what is actually said or written.
I could, for example, choose to read in your words all kinds of obtuse, racist propaganda, but that wouldn't in any way make you a racist.
Now, there are some items that even by the strictest Raw reading of both the item and all entries and articles related to it can equally support two contradictory positions. There are also those times where the RaW allows for something that doesn't seem like it would be the intended use. This is when clarification steps in, not ever changing the rules, but showing that of the two
equally (key word here) supported outcomes is 'official' and to say that 'Yes, that works this way, even though it seems it shouldn't, because of X.'
I just wish the various Sages had better understood their roles, and that more of them were actually
correct in their assessments of what the rules really state. Sure, it's good to know what the 'official' stance on suggested houserules are, or even what the writers wanted something to mean, but that really means exactly 0 if neither are actually supported by the rules.